Self-packaged optical interference display device having anti-stiction bumps, integral micro-lens, and reflection-absorbing layers

ABSTRACT

An electronic device of an embodiment of the invention is disclosed that at least partially displays a pixel of a display image. The device includes a first reflector and a second reflector defining an optical cavity therebetween that is selective of a visible wavelength at an intensity. The device includes a mechanism to allow optical properties of the cavity to be varied such that the visible wavelength and/or the intensity are variably selectable in correspondence with the pixel of the displayable image. The device also includes one or more transparent deposited films, one or more absorbing layers, an integral micro-lens, and/or one or more anti-stiction bumps. The deposited films are over one of the reflectors, for self-packaging of the device. The absorbing layers are over one of the reflectors, to reduce undesired reflections. The integral micro-lens is over one of the reflectors, and the anti-stiction bumps are between the reflectors.

BACKGROUND

Nearly all conventional displays are active in nature. This means thatpower must continually be supplied to the displays for them to maintainthe images they are displaying. Such conventional displays includedirect view and projection cathode-ray tube (CRT) displays, direct viewand projection liquid crystal displays (LCD's), direct view plasmadisplays, projection digital light processing (DLP) displays, and directview electroluminescent (EL) displays, among others.

Since power must continually be supplied to these types of displays,they can be a significant cause of power usage in devices where suppliedpower is at a premium, such as portable devices like laptop and notebookcomputers, personal digital assistant (PDA) devices, wireless phones, aswell as other types of portable devices. As a result, designers of suchdevices usually choose to increase the size of the battery sizecontained in such devices, increasing weight and cost, or choose toreduce the running time of the devices between battery charges.

For these and other reasons, therefore, there is a need for the presentinvention.

SUMMARY OF THE INVENTION

An electronic device of one embodiment of the invention at leastpartially displays a pixel of a display image. The device includes afirst reflector and a second reflector defining an optical cavitytherebetween that is selective of a visible wavelength at an intensity.The device includes a mechanism to allow optical properties of thecavity to be varied such that the visible wavelength and/or theintensity are variably selectable in correspondence with the pixel ofthe displayable image. The device also includes one or more transparentdeposited films, one or more absorbing layers, an integral micro-lens,and/or one or more anti-stiction bumps. The deposited films are over oneof the reflectors, for self-packaging of the electronic device. Theabsorbing layers are over one of the reflectors, to reduce undesiredreflections. The integral micro-lens is over one of the reflectors, andthe anti-stiction bumps are between the reflectors.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings referenced herein form a part of the specification.Features shown in the drawing are meant as illustrative of only someembodiments of the invention, and not of all embodiments of theinvention, unless otherwise explicitly indicated, and implications tothe contrary are otherwise not to be made.

FIG. 1A is a diagram of an electronic device for at least partiallydisplaying a pixel of a displayable image, according to an embodiment ofthe invention.

FIGS. 1B, 1C, and 1D are diagrams showing different approaches tocontrol the charge stored on the electronic device of FIG. 1A, accordingto varying embodiments of the invention.

FIGS. 2A and 2B are graphs of representative spectral responses of theelectronic device of FIG. 1A, according to varying embodiments of theinvention.

FIG. 3A is a diagram of an array of passive pixel mechanisms, accordingto an embodiment of the invention.

FIG. 3B is a cross-sectional diagram of a display device, according toan embodiment of the invention.

FIG. 4 is a method of use, according to an embodiment of the invention.

FIG. 5 is a diagram of an electronic device that is more specific thanbut consistent with the electronic device of FIG. 1A, according to anembodiment of the invention.

FIG. 6 is a method of manufacture, according to an embodiment of theinvention.

FIGS. 7A, 7B, and 7C are diagrams of electronic devices that are morespecific than but consistent with the electronic device of FIG. 1A,according to varying embodiments of the invention.

FIGS. 8A and 8B are diagrams of electronic devices that are morespecific than but consistent with the electronic device of FIG. 1A, andwhich include lenses, according to varying embodiments of the invention.

FIGS. 9A, 9B, and 9C are diagrams illustratively depicting howanti-stiction bumps can be fabricated within the electronic device ofFIG. 1A, according to an embodiment of the invention.

FIGS. 10A, 10B, and 10C are diagrams illustratively depicting howanti-stiction bumps can be fabricated within the electronic device ofFIG. 1A, according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of exemplary embodiments of theinvention, reference is made to the accompanying drawings that form apart hereof and in which is shown by way of illustration specificexemplary embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilized,and logical, mechanical, and other changes may be made without departingfrom the spirit or scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims.

Overview

FIG. 1A shows an electronic device 100 for at least partially displayinga pixel of a displayable image, according to an embodiment of theinvention. The device 100 includes a top reflector 102 and a bottomreflector 104, as well as a flexure 110 and a spring mechanism 112. Aresonant optical cavity 106 is defined by the reflectors 102 and 104,which has a variable thickness, or width, 108. The top reflector 102 isin one embodiment highly reflective, such as completely reflective. Thebottom reflector 104 is in one embodiment semi-transparent; that is, thebottom reflector 104 is in one embodiment semi-reflective. The springmechanism 112 may be a flexible material, such as a polymer, in oneembodiment of the invention, that has linear or non-linear springfunctionality.

The optical cavity 106 is variably selective of a visible wavelength atan intensity, by optical interference. Depending on the desiredconfiguration of the electronic device 100, the optical cavity 106 mayeither reflect or transmit the wavelength at the intensity. That is, thecavity 106 may be reflective or transmissive in nature. No light isgenerated by the optical cavity 106, such that the device 100 relies onambient light or light provided by the device 100 that is reflected ortransmitted by the cavity 106. The visible wavelength selected by theoptical cavity 106, and its intensity selected by the optical cavity106, are dependent on the thickness 108 of the cavity 106. That is, theoptical cavity 106 can be tuned to a desired wavelength at a desiredintensity by controlling its thickness 108.

The flexure 110 and the spring mechanism 112 allow the thickness 108 ofthe cavity 106 to vary, by allowing the bottom reflector 104 to move.More generally, the flexure 110 and the spring mechanism 112 constitutea mechanism that allows variation of the optical properties of theoptical cavity 106 to variably select a visible wavelength at anintensity. The optical properties include the optical index of thecavity 106, and/or the optical thickness of the cavity 106. A voltageapplied between the reflectors 102 and 104, or electrical charge storedon the reflectors 102 and 104, causes the thickness 108 of the cavity106 to change, because the flexure 110 and the spring mechanism 112allow the reflector 104 to move. Thus, the flexure 110 has a stiffness,and the spring mechanism 112 has a spring restoring force, such that thevoltage applied to the reflectors 102 and 104 or the charge stored onthe reflectors 102 and 104 causes the flexure 110 and the springmechanism 112 to yield and allow the reflector 104 to move, achievingthe desired thickness 108. No power is dissipated in maintaining a giventhickness 108.

In one embodiment, the bottom reflector 104 is maintained at a fixedvoltage, and the top reflector 102 is set to a voltage depending on thedesired visible wavelength and the desired intensity, as calibrated tothe stiffness of the flexure 110. Whereas the flexure 110 is shown inthe embodiment of FIG. 1A as positioned under the bottom reflector 104,in another embodiment it may be positioned over the bottom reflector104. In other embodiments, the flexure 110 may be positioned over orunder the top reflector 102 as well, such that the bottom reflector 104is movable instead of the top reflector 102, to adjust the thickness 108of the optical cavity 106. Furthermore, in another embodiment, there maybe more than one optical cavity, such that the optical cavity 106 isinclusive of more than one such cavity.

In one embodiment, the bottom reflector 104 and the top reflector 102can be considered the plates of a capacitor, where the optical cavity106 represents the dielectric therebetween. A potential applied betweenthe bottom reflector 104 and the top reflector 102 moves the bottomreflector 104, due to the flexure 110 and the spring mechanism 112, butalso causes a charge to be stored in the capacitor. It is thiselectrostatic charge that then allows maintenance of the given thickness108 without any further voltage application over the bottom reflector104 and the top reflector 102.

The wavelength and the intensity selected by the optical cavity 106correspond to a pixel of a displayable image. Thus, the electronicdevice 100 at least partially displays the pixel of the image. Theelectronic device 100 can operate in either an analog or a digitalmanner. As an analog device, the electronic device 100 selects a visiblewavelength of light and an intensity corresponding to the color and theintensity of the color of the pixel. In an alternative embodiment, theelectronic device 100 may be used to display the pixel in an analogmanner in black-and-white, or in gray scale, in lieu of color.

As a digital device, the electronic device 100 is responsible for eitherthe red, green, or blue color component of the pixel. The device 100maintains a static visible wavelength, either red, green, or blue, andvaries the intensity of this wavelength corresponding to the red, green,or blue color component of the pixel. Therefore, three of the device 100are needed to display the pixel digitally, where one device 100 selectsa red wavelength, another device 100 selects a green wavelength, and athird device 100 selects a blue wavelength. More generally, there is adevice 100 for each color component of the pixel, or portion, of theimage. Furthermore, in an alternative embodiment, the electronic device100 may be used to display the pixel in a digital manner inblack-and-white, or in gray scale, in lieu of color.

Optical Interference to Variably Select Wavelength and Intensity

The optical cavity 106 of the electronic device 100 utilizes opticalinterference to transmissively or reflectively select a wavelength at anintensity. The optical cavity 106 in one embodiment is a thin filmhaving a light path length equal to the thickness 108. Light isreflected from the boundaries of the reflectors 102 and 104 on eitherside of the cavity 106, interfering with itself. The phase differencebetween the incoming beam and its reflected image is k(2d), where d isthe thickness 108, because the reflected beam travels the distance 2dwithin the cavity 106. Since ${k = \frac{2\pi}{\lambda}},$then when ${d = \frac{\lambda}{2}},$the phase difference between the incoming and the reflected waves isk2d=2π, giving constructive interference. All multiples of π/2, whichare the modes of the optical cavity 106, are transmitted. As a result ofoptical interference, then, the optical cavity 106 passes the most lightat integer multiples of λ/2, and the least amount of light at oddinteger multiples of λ/4. Although the above calculations capture theprimary mechanism for interference-based light modulation, more rigorouselectromagnetic simulations may be desired to more accurately describeactual device performance.

In one embodiment, the top reflector 102 includes a thin, partiallytransmitting metallic film, where n−ik=2.5−2.5i titanium, where nrepresents the real optical index of the cavity 106, and k representsthe imaginary optical index of the cavity 106. In this embodiment, bothabsorption and interference play roles in modulating the color andintensity of the output. The optical cavity 106 is an adjustable spacer,and the bottom reflector 104 is a high-reflectance metallic substrate,like aluminum. In one embodiment, where the device 100 is digital, theoptical cavity 106 may select a red wavelength of 6100 angstrom (Å), agreen wavelength of 5500 Å, or a blue wavelength of 4500 Å, at anintensity depending on the corresponding color component of the pixel tobe displayed. Furthermore, the optical cavity 106 can achieve lowreflection or transmission. In this latter state, the optical cavity 106is a so-called “dark mirror” that can be optimized for less than fivepercent reflection or transmission.

For example, in this embodiment, the film stack sequence of the bottomreflector 104, the optical cavity 106, and the top reflector 102 canachieve a red wavelength of 6100 Å, with an incident n of 1.5 at thebottom reflector 104 and a substrate n of 1.52 at the top reflector 102in accordance with the following table: Real Target Number of indexImaginary Thickness wavelength waves at Layers (n) index (k) (Å)intensity target Bottom 0.2 5 6250 5000 0.25 reflector 104 (silver)Optical 1 0 2750 5000 0.55 cavity 106 Top 2.5 2.5 200 5000 0.1 reflector102 (titanium)

Similarly, this film stack sequence can achieve a green wavelength of5500 Å with an incident n of 1.5 at the top reflector 102 and asubstrate n of 1.52 at the bottom reflector 104 in accordance with thefollowing table: Real Target Number of index Imaginary Thicknesswavelength waves at Layers (n) index (k) (Å) intensity target Bottom 0.25 6250 5000 0.25 reflector 104 (silver) Optical 1 0 2500 5000 0.5 cavity106 Top 2.5 2.5 200 5000 0.1 reflector 102 (titanium)

The film stack sequence can also achieve a blue wavelength of 4500 Åwith an incident n of 1.5 at the top reflector 102 and a substrate n of1.52 at the bottom reflector 104 in accordance with the following table:Real Target Number of index Imaginary Thickness wavelength waves atLayers (n) index (k) (Å) intensity target Bottom 0.2 5 6250 5000 0.25reflector 104 (silver) Optical 1 0 2000 5000 0.5 cavity 106 Top 2.5 2.5200 5000 0.1 reflector 102 (titanium)Thus, the film stack sequence achieves a red wavelength of 6100 Å, agreen wavelength of 5500 Å, or a blue wavelength of 4500 Å, depending onwhether the thickness of the optical cavity 106 is 2750 Å, 2500 Å, or2000 Å, respectively.

Finally, the film stack sequence can achieve a low reflection or a lowtransmission with an incident n of 1.5 at the top reflector 102 and asubstrate n of 1.52 at the bottom reflector 104 in accordance with thefollowing table: Real Target Number of index Imaginary Thicknesswavelength waves at Layers (n) index (k) (Å) intensity target Bottom 0.25 6250 5000 0.25 reflector 104 (silver) Optical 1 0 400 5000 0.08 cavity106 Top 2.5 2.5 200 5000 0.1 reflector 102 (titanium)This results in dark gray, nearly black output, where the thickness ofthe optical cavity 106 is 400 Å. By ratioing the amount of time that apixel remains in the colored or black states, a large range of averagehues and intensities can be obtained.Controlling Thickness of Optical Cavity

As has been indicated, the flexure 110 and the spring mechanism 112allow the thickness 108 of the optical cavity 106 to vary when anappropriate voltage has been applied across the reflectors 102 and 104,such that a desired wavelength at a desired intensity is selected. Thisvoltage is determined in accordance with the following equation, whichis the force of attraction between the reflectors 102 and 104 acting asplates of a parallel plate capacitor, and which does not take intoaccount fringing fields: $\begin{matrix}{{F = \frac{ɛ_{0}V^{2}A}{2d^{2}}},} & (1)\end{matrix}$where ∈₀ is the permittivity of free space, V is the voltage across thereflectors 102 and 104, A is the area of each of the reflectors 102 and104, and d is the thickness 108. Thus, a one volt potential appliedacross a 100 micron square pixel, with a thickness 108 of 0.25 micron,yields an electrostatic force of 7×10⁻⁷ Newton (N).

Therefore, a small voltage between the reflectors 102 and 104 providessufficient force to move the bottom reflector 104, and hold it againstgravity and shocks. Once the voltage has been applied, the electrostaticcharge stored in the capacitor created by the reflectors 102 and 104,and defining the cavity 106, is sufficient to hold the bottom reflector104 in place without additional power. Charge leakage may requireoccasional refreshing of the charge, however.

The force defined in equation (1) is balanced with the linear springforce provided by the spring mechanism 112:F=k(d ₀ −d),  (2)where k is the linear spring constant, and d₀ is the initial value ofthe thickness 108. The range in which the forces of equations (1) and(2) are in stable equilibrium occurs when the value (d₀−d) is betweenzero and d₀/3. At ${{d_{0} - d} > \frac{d_{0}}{3}},$the electrostatic force of attraction of equation (1) overcomes thespring force of equation (2), such that the reflector 104 snaps to thereflector 102, which is undesirable. This occurs because when thereflector 104 is beyond the d₀/3 position, excess charge is drawn ontothe reflectors 102 and 104 due to increased capacitance, which in turnincreases the attractive force of equation (1) between the reflectors102 and 104, causing the reflector 104 to pull towards the reflector102.

To overcome this limitation, the force between the reflectors 102 and104 of equation (1) can instead be written as a function of charge:$\begin{matrix}{{F = \frac{- Q^{2}}{2\quad ɛ\quad A}},} & (3)\end{matrix}$where Q is the charge on the capacitor. Thus, the force F is now not afunction of the distance d, and stability of the reflector 104 can existover the entire range of 0 to d₀. By limiting the amount of charge onthe reflectors 102 and 104, in other words, the position of thereflector 104 can be set over the entire range of travel.

Although the description of the preceding paragraphs is with respect toan ideal parallel-plate capacitor and an ideal linear spring restoringforce, those of ordinary skill within the art can appreciate that theprinciple described can be adapted to other configurations, such asnon-linear springs and other types of capacitors. Eliminating orreducing the range of operation where snap down of the reflector 104against the reflector 102 occurs enables more practical analogoperation, or non-contact discrete operation, without limiting thenumber of colors as may otherwise occur when snap down occurs. That is,because the usable range is increased, more colors, saturation levels,and intensities can be achieved.

In addition, in one embodiment, the range within which non-contactoperation can occur without snap down may be increased by constructingthe flexure 110 in a particular manner. The particular manner is suchthat the restoring force of the spring mechanism 112 is a non-linearfunction of the displacement of the flexure 110, and increases at afaster rate than the displacement. This can be achieved by increasingthe thickness of the flexure 110, or by using a flexure that is firstbent and then stretched, which is known as a “bend and stretch” design.

Furthermore, the device 100 can be operated at smaller values of thethickness 108, allowing a black state to be achieved without any portionof the reflectors 102 and 104 coming into contact with one another. Thisprevents stiction and the accompanying hysteresis that occurs when thereflectors 102 and 104 contact one another. Even if the reflectors 102and 104 are allowed to contact one another, the voltage differencebetween the reflectors 102 and 104 will be less where the amount ofcharge on the reflectors 102 and 104 is specifically controlled (thatis, where a predetermined amount of fixed charge is controlled), asopposed to where the voltage between the reflectors 102 and 104 isspecifically controlled. This advantageously reduces electrostaticbreakdown in the dielectric separating the reflectors 102 and 104 thatdefines the optical cavity 106, as well as reducing the electrostaticforce between the reflectors 102 and 104 that would otherwise increasestiction, and the wear on any anti-stiction standoffs employed to reducethe surface area between the reflectors 102 and 104.

Controlling Charge on Reflectors

FIGS. 1B, 1C, and 1D show different approaches to control the amount ofcharge on the reflectors 102 and 104 of the electronic device 100, asopposed to specifically controlling the voltage between the reflectors102, and 104, according to varying embodiments of the invention. As hasbeen described in the preceding section of the detailed description, thethickness 108 between the reflectors 102 and 104 can be regulated bycontrolling the charge stored on the reflectors 102 and 104. Thereflectors 102 and 104 thus act as the plates of a parallel platecapacitor.

In FIG. 1B, a controlled, or predetermined, amount of charge is injectedonto the reflectors 102 and 104 by integrating a known current for aknown time, utilizing the current integration mechanism 120 electricallycoupled to the reflectors 102 and 104. The current, I, the time, t, orboth the current and the time can thus be manipulated to yield thedesired amount of charge. The mechanism 120 may include a currentsource, a digital-to-analog current source, and/or time divisioncircuitry to create the desired level of charge.

In FIG. 1C, the charge available to the reflectors 102 and 104 islimited to prevent snap down of the reflectors 102 and 104 together.This is specifically accomplished in one embodiment of the invention byutilizing a voltage divider circuit 129. The circuit 129 includes avoltage source 130 placed in series with a capacitor 134. A switch 132controls the on-off operation of the circuit 129. A switch 136, placedin parallel with the voltage source 130 and the capacitor 134, acts as areset switch, which may be utilized to avoid voltage or charge driftover time, due to charge leakage. The reset is desirably performed morequickly than the mechanical response time of the circuit 129.

Where the flexure 110 is linear, the range of stable travel can beextended through the entire initial thickness 108 of the optical cavity106 if C<C′_(init)/2, where C is the capacitance of the capacitor 134,and C′_(init) is the initial capacitance of the variable capacitorformed by the reflectors 102 and 104, and the optical cavity 106. As thevoltage of the voltage source 130 increases, the resulting charge isshared between the variable capacitor and the capacitor 134 to at leastsubstantially eliminate snap down. As can be appreciated by those ofordinary skill within the art, this principle can be applied to otherconfigurations than a parallel plate capacitor and a linear springrestoring force, such as non-linear springs, and capacitors other thanparallel plate capacitors.

In FIG. 1D, the charge on the reflectors 102 and 104 is controlled byusing an approach referred to as fill-and-spill, utilizing afill-and-spill circuit 131. The switch 136 is closed and opened todischarge the variable capacitor formed by the reflectors 102 and 104,and the optical cavity 106. The switch 138 of the circuit 131 is thenopened and the switch 132 is closed, to charge the fixed capacitor 134.That is, the capacitor 134 is “filled.” Next, the switch 132 is openedand the switch 138 is closed, so that the capacitor 134 shares itscharge with the variable capacitor. That is, the capacitor 134 “spills”its charge. The charge on the reflectors 102 and 104 reaches a stablevalue, even though it depends on the thickness 108 of the optical cavity106. The voltage source 130 has thus provided a controlled charge tomaintain the desired thickness 108.

Higher-order Gaps

The optical interference as described in the preceding sections of thedetailed description to transmissively or reflectively selectwavelengths at desired intensities relies upon first-order gaps in oneembodiment of the invention. That is, the gap of the optical cavity 106,which is the thickness 108 of the optical cavity 106, is regulated so asto control the interference first-order wavelengths of light. However asthe thickness 108 of the optical cavity 106 increases, reflectance peaksshift to longer wavelengths, and additional, higher order, peaks moveinto the spectral region.

The spectral bandwidth of the electronic device 100 is determined by theoptical constants of the films utilized for the reflectors 102 and 104,their thicknesses, and the thickness 108 of the optical cavity 106between the reflectors 102 and 104. In such instances, the electronicdevice 100 functions as a so-called Fabry-Perot-based light modulator.The spectral purity, or saturation, of the reflected light is determinedby the spectral bandwidth of the device 100, and tradeoffs may have tobe made between peak reflectance, spectral bandwidth, black statereflectance, and optical efficiency of the white state.

Peak reflectance occurs for reflective Fabry-Perot modulators when:2nd=mλ,  (4)where, as before, n is the gap index, d is the thickness 108 of theoptical cavity 106, m is a non-negative integer specifying theinterference order, and λ is the wavelength of light. Equation (4) thusspecifies a simple model of interference. It is noted that the actualreflectance spectra may be more accurately modeled by performingrigorous electromagnetic simulations, involving all material constantsand interfaces within the device 100, as can be appreciated by those ofordinary skill within the art of optical thin films.

The higher-order peaks exhibit a narrower spectral bandwidth and thusincreased saturation. The spectral bandwidth of the green state isparticularly significant in determining saturation, since thewavelengths in and around the green wavelengths overlap the blue and redsensitivity curves of the human eye. The red and blue saturation may beimproved by shifting the peak spectral wavelength away from the adjacentcolor-response curves and into the relatively insensitive portion of thespectrum, which is not possible with green. Narrowing the spectralbandwidth to increase the green saturation therefore has the problem oflimiting the brightness of the display, since the peak sensitivity ofthe human eye is in the green region, leading to a reduced white leveland lower overall contrast.

To overcome this limitation, the thickness 108 may be increased toproduce second-order, or more generally higher-order, color, rather thanfirst-order color. FIG. 2A shows a graph 220 of a representativefirst-order green spectral response 226 and a representative greensecond-order spectral response 228, according to an embodiment of theinvention. The y-axis 224 denotes reflectance as a function ofwavelength on the x-axis 222. The second-order response 228 has anarrower spectral bandwidth and improved color saturation. Thus, thesecond-order response 228 can be utilized in one embodiment of theinvention in lieu of the first-order response 226 for increasedsaturation and color component. In another embodiment, the second-orderresponse 228 is utilized for increased saturation, whereas thefirst-order response 226 is utilized for increased brightness and whitelevel.

Color saturation is typically improved for second-order responses forblue through green. FIG. 2B shows a graph 240 of a second-order bluespectral response 242, according to an embodiment of the invention. Thegraph 240 has the y-axis 224 denoting reflectance as a function ofwavelength on the x-axis 222, as before. The second-order blue response242 provides for increased saturation, as compared to using afirst-order blue spectral response. However, the second-order redspectral response 244 is less useful, because the third-order bluespectral response 246 begins to enter the visible spectral range.

Display Device and Method of Use Thereof

FIG. 3A shows an array of passive pixel mechanisms 200, according to anembodiment of the invention. The passive pixel mechanisms 200 includethe mechanisms 200A, 200B, . . . , 200N, organized into columns 202 androws 204. Each of the pixel mechanisms 200 is able to variably select avisible wavelength at an intensity by optical interference andabsorption, in correspondence with a displayable image. The pixelmechanisms 200 can be considered the apparatus for performing thisfunctionality in one embodiment of the invention. The mechanisms 200 arepassive in that they do not generate light by themselves, but ratherreflect or transmit ambient and/or supplemental light.

In one embodiment, each of the passive pixel mechanisms 200 includes oneor more of the electronic device 100. Thus, a pixel may include one ormore of the device 100. Where the passive pixel mechanisms 200 displaytheir corresponding pixels of the displayable image in an analog manner,each of the mechanisms 200 may include only one electronic device 100,because the single device 100 is able to display substantially any colorat any intensity. Where the mechanisms 200 display their correspondingpixels in a digital manner, each of the mechanisms 200 may include threeof the electronic devices 100, one for each of the red color component,the green color component, and the blue color component.

FIG. 3B shows a cross-sectional profile of a display device 300,according to an embodiment of the invention, which incorporates thearray of passive pixel mechanisms 200. An optional supplemental lightsource 304 outputs light for reflection by the mechanisms 200. Where thelight source 304 is present, the mechanisms 200 reflect both the lightprovided by the source 304, as well as any ambient light. Where thelight source 304 is absent, the mechanisms 200 reflect ambient light.The light source 304 is indicated in the embodiment of FIG. 3B such thatit outputs light for reflection by the mechanisms 200. In anotherembodiment, the light source 304 may be behind the mechanisms 200, suchthat the mechanisms 200 transmit light output by the source 304.

A controller 302 controls the pixel mechanisms 200, effectivelyproviding a pixilated displayable image to the pixel mechanisms 200.That is, in the embodiment where the mechanisms 200 each include one ormore of the electronic device 100, the controller 302 changes thethickness 108 of the cavity 106 of each device 100, so that the image isproperly rendered by the pixel mechanisms 200, for display to a user308. The controller 302 thus electrically or otherwise adjusts thethickness 108 of the optical cavity 106, where, once adjusted, thethickness 108 is maintained by the flexure 110.

The controller 302 may receive the displayable image from an imagesource 306 in a pixilated or a non-pixilated manner. If non-pixilated,or if pixilated in a manner that does not correspond on a one-to-onebasis to the array of passive pixel mechanisms 200, the controller 302itself divides the image into pixels corresponding to the array ofpassive pixel mechanisms 200. The image source 306 itself may beexternal to the display device 300, as in the embodiment of FIG. 3B, orinternal thereto. The image source 306 may thus be a desktop computerexternal to the display device 300, or may be a laptop or notebookcomputer, personal digital assistant (PDA) device, wireless phone, orother device of which the display device 300 is a part.

FIG. 4 shows a method of use 400, according to an embodiment of theinvention, for a display device, such as the display device 300 of FIG.3B. First, a displayable image is divided into pixels (402), resultingin a pixilated displayable image. Light is optionally provided (404), tosupplement any ambient light. For each pixel of the image, acorresponding visible wavelength is selected, at a correspondingintensity, by optical interference and absorption (406), as has beendescribed. The corresponding wavelength at the corresponding intensitymay be selected in a digital or an analog manner, as has also beendescribed.

Specific Electronic Device and Method of Manufacture Thereof

FIG. 5 shows a pair of electronic devices 500A and 500B for at leastpartially displaying a corresponding pair of pixels of a displayableimage, according to an embodiment of the invention. Each of theelectronic devices 500A and 500B is a specific embodiment of theelectronic device 100 of FIG. 1A, and thus the description of FIG. 1A isequally applicable to FIG. 5 as well. Furthermore, the electronicdevices 500A and 500B can each be used to realize each of the passivepixel mechanisms 200 of FIG. 3A, in one embodiment of the invention. Thefollowing description of FIG. 5 is made with specific reference to theelectronic device 500A, but is identically applicable to the electronicdevice 500B. Furthermore, FIG. 5 is not drawn to scale, for illustrativeclarity.

The bottom reflector 104 is positioned over a silicon substrate 502, andmore generally is a conductive reflective layer. A thin dielectric 504is present over the bottom reflector 104 to prevent shorting of thereflector 102. The optical cavity 106 is defined between the topreflector 102 and the bottom reflector 104, where the top reflector 102is also more generally a conductive reflective layer. The flexure 110,positioned over the top reflector 102, is also referred to as a flexurelayer, and acts as a flexible electrode for the top reflector 102, aswell as maintains tension on the top reflector 102 and allows thereflector 102 to move. The spacing of the optical cavity 106 can becontrolled by calibrating voltage to the stiffness of the flexure 110 inan analog mode, or by providing stops of varying thickness for red,green, and blue pixels in a digital mode.

A dielectric pixel plate 506, which may be oxide, partially covers theflexure 110 and the top reflector 102. In one embodiment, the dielectricpixel plate 506 may have a width 508 between 40 and 100 micron, and canhave a height 510 of between three and five micron. An air cavity 514surrounds the dielectric pixel plate 506, and is larger than thecoherence length of the optical cavity 106 to prevent additionalinterference effects. The air cavity 514 in one embodiment may have aheight 520 of between three and five micron. The oxide 512 and 518represent an additional layer used to define the air cavity 514, wherein one embodiment the oxide 518 may also have a height 522 of betweenthree and five micron.

The via hole 516 is used to allow removal of material from the aircavity 514 and the optical cavity 106. For instance, polysilicon oranother filler material may be deposited to reserve space for the aircavity 514 and the optical cavity 106, but then is removed to actuallyform the cavities 514 and 106. A protective layer 524 covers the oxide518, and an anti-reflective coating (ARC) 526 covers the protectivelayer 524. The ARC 526 is desirable to avoid unwanted coherentinteractions within the optical cavity 106 itself.

FIG. 6 shows a method 600 for manufacturing an electronic device, suchas the electronic device 500A or 500B of FIG. 5, or a display devicehaving a number of such electronic devices, according to an embodimentof the invention. First, a bottom metal reflector layer is provided on asilicon substrate layer (602). This may include depositing andpatterning the bottom metal reflector layer. In FIG. 5, the bottom metalreflector layer is the bottom reflector 104. Next, an oxide dielectriclayer is deposited (604), which in FIG. 5 is the thin dielectric 504.

Polysilicon or a different filler material is deposited and patterned(604). The polysilicon acts as a placeholder for the resonant opticalcavity to be formed. In FIG. 5, the polysilicon thus occupies the spaceof the optical cavity 106. A flexure layer and a top metal reflectorlayer are then provided on the polysilicon (608). This can includedepositing the flexure layer first and then the top metal reflectorlayer, or vice-versa, and patterning the flexure layer and the top metalreflector layer. In FIG. 5, the flexure layer is the flexure 110,whereas the top metal reflector layer is the top reflector 102.

An oxide pixel plate layer is provided on the flexure layer and the topmetal reflector layer (610). This can include depositing the oxide andpatterning the oxide. In FIG. 5, the oxide pixel plate layer is thedielectric pixel plate 506. Additional polysilicon or additional fillermaterial is then deposited on the oxide pixel plate layer and patterned(612), to act as a placeholder for an air cavity to be formed. In FIG.5, the polysilicon thus occupies the space of the air cavity 514. Anoxide layer is deposited on this polysilicon (614), which in FIG. 5 isthe oxide 518 and 512.

Next, a via hole is defined through the polysilicon (616), which isrepresented in FIG. 5 as the via hole 616. The polysilicon that has beenpreviously deposited is then removed to define the resonant opticalcavity and the air cavity (618). For instance, the removal can beconducted by performing isotropic polysilicon cleanout etching. In FIG.5, this results in formation of the optical cavity 106 and the aircavity 514. Finally, a protective layer is provided over the oxide layer(620), and an anti-reflective coating is provided over the protectivelayer (622). In FIG. 5, the protective layer is the protective layer524, and the anti-reflective coating is the anti-reflective coating 526.

Additional Specific Electronic Devices

FIGS. 7A and 7B shows the electronic device 100 of FIG. 1A, according toa specific embodiment of the invention. The description of FIG. 1A isthus applicable to FIGS. 7A and 7B as well. The electronic device 100 ofthe embodiment of FIGS. 7A and 7B is more generally a Fabry-Perot-baseddevice. The sawing and packaging of optical micro-electrical mechanicalsystem (MEMS) devices, such as micro-mirrors, Fabry-Perot devices, anddiffraction-based devices, can be difficult because of the fragility ofthe MEMS components, and the need for a transparent package. MEMS aregenerally semiconductor chips that have a top layer of mechanicaldevices, such as mirrors, fluid sensors, and so on. Wafer sawing is awet process that can damage and/or contaminate the delicate devices uponrelease. Releasing the devices from sacrificial layers after sawing isdifficult and costly if performed on a die-by-die basis. Packaging ofsuch devices usually includes bonding a glass window to a package on aceramic or other substrate, which can be costly, difficult to perform,and may add considerable size to the device. The electronic device 100of the embodiment of FIGS. 7A and 7B overcomes these problems.

Referring first to FIG. 7A, a sacrificial material 704 is deposited overthe movable components of the device 100, including the flexure 110, thereflective layers 102 and 104 that define the optical cavity 106, andthe spring mechanism 112 that have been described. A layer 702 isdeposited over and makes contact with this substrate at the locationsindicated by the reference number 708. Openings 706 are patterned andetched in the layer 702. The device 100 is released by isotropicallyetching away the sacrificial material 704, using selective releasechemistries known within the art, which may be dry or wet processes.

Referring next to FIG. 7B, a material 710 is then deposited into theopenings, or vias, 706, to provide a sealed environment for the device100. The layer 702 and the material 710 can be transparent dielectrics,or multi-layer films. The material 710 can perform a dual role as bothan anti-reflective coating, and a sealing layer. Where techniques suchas physical vapor deposition (PVD) or chemical vapor deposition (CVD)are utilized, a vacuum or hermetic environment can be achieved.Utilizing CVD at higher pressures can be employed where ahigher-pressure environment is utilized.

The material 710 is optional, however, if a hermetic seal is notdesired. Even without the material 710, some protection for the device100 is achieved, as non-hermetic seals also help to protect the device100 from water, contaminants, and particulates. If the material 710 isused to seal the openings 706, but is not desired over the entiresurface, it may be patterned and etched away using lithographictechniques known within the art.

Furthermore, the process described in relation to FIGS. 7A and 7Benables encapsulation within a clean-room environment withoutconventional packaging, such that the process may be described asself-packaging. Because the process is preferably performed in aclean-room environment, and the release operation occurs inside aprotective cavity, increased yields can result. Once the cavities aresealed the die can be sawed off, as known within the art, withoutdamaging the device 100.

FIG. 7C shows the electronic device 100 of FIG. 1A, according to anotherspecific embodiment of the invention. The description of FIG. 1A is thusapplicable to FIG. 7C as well. It is noted that the ratio of the activelight modulator area to the non-active area is referred to as theaperture ratio. The non-active area includes the space between pixels,support posts, the flexure area, and so on. Light reflected from thenon-active area can increase the black state reflectance, reducingoverall system contrast. The electronic device 100 of the embodiment ofFIG. 7C reduces this effect by including an absorbing layer, or bordermask, 722 to cover such non-active areas. The self-packaging material710 that has been described in conjunction with FIG. 7B provides asubstrate for the border mask 722. Other like-numbered components ofFIG. 7C relative to FIGS. 7A and 7B are identical to their counterpartsof FIGS. 7A and 7B, and are not re-described in relation to FIG. 7C.

The border mask 722 may be composed of a variety of different materials,including absorptive polymers, photo-imageable absorptive polymers,metal and/or dielectric composites, and/or interference-based inducedabsorbers. Absorptive polymers are typically spun on and imaged with aphotoresist mask and develop process. Photo-imageable polymers can bepatterned directly with lithographic techniques known within the art.Metal and/or dielectric composites known as cermets are other materialsthat can be used, and have typically been developed for use as solarabsorbers. Such materials include black molybdenum, black tungsten, andblack chrome, and have very high absorbance. Further, they can bedeposited with sputtering or evaporation techniques known within theart. Induced absorbers maximize the absorbance within a dissipatinglayer, by tuning layer thickness. Induced absorbers are relatively thin,such as less than 1000 Å.

The electronic device 100 of the embodiment of FIG. 7C lends itself to athree-state operation having dedicated pixel types. For instance, theremay be a type-one three-state pixel, having the color states red, green,and black, or there may be a type-two three-state pixel, having thecolor states red, blue, and black. There may also be a type-threethree-state pixel, having the color states green, blue, and black. Thus,the configuration of this operation includes groups of three-statepixels. Different pixels in the group are designed to operate withdifferent states. The different color states are controlled by thethickness of the sacrificial material 704. Such a configuration can beoperated in a digital mode, with one pixel plate, or reflector, state ina non-contact position, and the other two states in contact with eitherthe top or bottom capacitor plates, or reflectors. This has theadvantage over a single-gap, two-state, configuration by allowing acolor to be produced by two of the three pixels, instead of one of thethree pixels, leading to brighter colors.

The electronic device 100 of the embodiment of FIG. 7C also lends itselfa dual-gap, dual-capacitor pixel design, which is characterized by thereflector 102 moving forming two variable capacitors, as is nowdescribed. A layer 720 is a partial reflector on the underside of thelayer 702, and is over the reflector 102. The layer 720 acts as both apartial reflector and as a capacitor plate. The reflector 102 may bedriven up towards the layer 720, or down towards reflector, or capacitorplate, 104 electrostatically. The spring mechanism 112 thus is deflectedin two directions and needs to travel only about half as far from itsequilibrium position to cover the same total travel as when deflected injust one direction. This increased travel range enables modes ofoperation where pixels can produce multiple colors, multiplesaturations, and black. The cavity made by removing the sacrificialmaterial 106 serves as one gap, and the optical cavity 704 serves asanother gap in this design.

Such a design can function in at least two different modes of operation.For example, in one mode of operation, individual pixels are capable ofcreating multiple colors and intensities as needed for color displays.The pixels operate in contact mode at one or both of the gap extremes,and otherwise operate in on-contact mode. As another example, in anothermode of operation, multiple hues and intensities can be achieved withoutoperating in contact mode.

Furthermore, the electronic device 100 of any of the embodiments ofFIGS. 7A, 7B, and 7C lends itself to single-gap, dual-mode (or,multi-level) operation, where the modes include contact between thereflectors 102 and 104, and non-contact between the reflectors 102 and104. Each pixel is capable of creating multiple colors and intensitiesas needed for color displays. The pixels operate in a contact mode atone gap extreme, and in a non-contact mode for the remaining states.

When pixels are dedicated to specific hues, such as red, green, andblue, optical efficiency may be reduced, since pixels of the wrong colorcannot be used to generate the desired color. Therefore, it isadvantageous to control the pixel gap, which is the thickness 108 ofFIG. 1A that has been described, in a non-contact mode, such as ananalog mode, a multi-level digital mode, or a combination analog anddigital mode. The device 100 may need the thickness 108 to be less than1000 Å to create black, about 1800 Å to create blue, and about 2800 Å tocreate red. To provide such different thicknesses, a single-gap, voltagecontrol mode of operation that can be utilized is to operate in anon-contact mode between red and blue, and then allow the pixel to snapto the black state in a digital mode.

FIGS. 8A and 8B show a pair of electronic devices 800A and 800B for atleast partially displaying a corresponding pair of pixels of adisplayable image, according to varying embodiment of the invention.Each of the electronic devices 800 and 800B is a specific embodiment ofthe electronic device 100 of FIG. 1A, and thus the description of FIG.1A is equally applicable to FIGS. 8A and 8B as well. It is noted that aspixel size is reduced, a smaller aperture ratio usually results.Like-numbered components of FIGS. 8A and 8B relative to FIGS. 1A and7A-7C are identical, and are not otherwise described with respect toFIGS. 8A and 8B. Further, for illustrative clarity only, not allcomponents of FIGS. 1A and 7A-7C are shown in FIGS. 8A and 8B.

In FIG. 8A, the disadvantage of reduced aperture ratio is overcome bythe electronic devices 800 and 800B by employing integral lenses 804Aand 804B applied directly to the monolithic MEMS devices 800 and 800B,using coating or depositional techniques. The self-packaging layer 702provides a substrate for these micro-lenses 804A and 804B, after aninitial layer 802 has been deposited. The lenses 804A and 804B can beformed by patterning photoresist or other photo-imageable polymer usingknown lithographic techniques, and then partially flowing the patternsto the desired lens profile with heat treatment. The polymer may remainas the final lenses, or can be used as a mask to transfer the lenspattern to the underlying layer 802 with plasma or reactive-ion etching.The lenses 804A and 804B can be made more efficient by matching theshape thereof to the underlying pixels.

In FIG. 8B, the self-packaging layer 702 is itself used as a simple formof a micro-lens. Such a technique relies on the coverage of thedeposition over the reflector 102 to form a lensing action over thenon-active region of the pixel where needed. For the layer 702 toeffectively act as a lens, deposition thickness, pixel gap spacing, andpixel plate, or reflector, thickness and profile are desirablyoptimized. The advantage to the approach of FIG. 8B is that noadditional lens is needed, and the lensing action is present only whereit is needed, around the non-active region of the pixels.

Anti-stiction Bumps

When two surfaces come into contact, they are frequently attracted toone another by a variety of different forces, such as Van Der Waalsattractive forces, chemical bonding forces, capillary forces, andCasimir forces. These forces often lead to surfaces that cannot beseparated once they come into contact. Therefore, to prevent thereflectors 102 and 104 of the electronic device 100 from coming intocontact with one another, in one embodiment of the inventionanti-stiction bumps are placed on the bottom reflector 104 prior tofabrication of the top reflector 102.

FIGS. 9A, 9B, and 9C illustratively depict the manner by whichanti-stiction bumps can be fabricated on the bottom reflector 104,according to one embodiment of the invention. In FIG. 9A, the flexure110 and the bottom reflector 104 of the electronic device 100 arealready present. A sacrificial material 902 is deposited, and then, inFIG. 9B, is patterned and partially etched to yield recesses 904.Subsequent layers, such as the layer 906 in FIG. 9C, are thensubsequently deposited into the recessions 904 to yield bumps 908 withinthe recessions 904.

FIGS. 10A, 10B, and 10C illustratively depict the manner by whichanti-stiction bumps can be fabricated on the bottom reflector 104,according to another embodiment of the invention. In FIG. 10A, theflexure 110 and the bottom reflector 104 of the electronic device 100are already present, as before. A first sacrificial material 910 isdeposited that has the same thickness of the desired anti-stiction bumpheight. The material 910 is patterned and etched to yield the recesses912. In FIG. 10B, a second sacrificial material 914 is deposited toachieve the total sacrificial layer thickness. Finally, in FIG. 10C,subsequent layers, such as the layer 916, are deposited into therecessions 912 to yield bumps 918 within the recessions 912.

Conclusion

It is noted that, although specific embodiments have been illustratedand described herein, it will be appreciated by those of ordinary skillin the art that any arrangement is calculated to achieve the samepurpose may be substituted for the specific embodiments shown. Thisapplication is intended to cover any adaptations or variations of thepresent invention. For example, whereas embodiments of the inventionhave primarily been described as relating to a direct display device,other embodiments are applicable to a projection display device, suchthat the terminology of displaying a pixel references both of these, aswell as additional, such display scenarios. For instance, in projectionapplications, the pixel size may be on the order of ten-to-twentymicrons. Therefore, it is manifestly intended that this invention belimited only by the claims and equivalents thereof.

1.-31. (canceled)
 32. A method for manufacturing a device for at leastpartially displaying a pixel of a displayable image comprising:providing a bottom metal reflector layer on a substrate layer of thedevice; depositing and patterning first filler material on the bottommetal reflector layer; providing a flexure layer and a top metalreflector layer on the first filler material; providing an oxide pixelplate layer on the flexure layer and the top metal reflector layer;depositing and patterning second filler material on the oxide pixelplate layer; depositing an oxide layer on the second filler material;defining a via through the second filler material; and, removing thefirst filler material to define an optical cavity between the first andthe top metal reflector layers, and the second filler material to definean air cavity between the oxide pixel plate layer and the oxide layer.33. The method of claim 32, further comprising, after providing thebottom metal reflector layer, depositing an oxide dielectric layer. 34.The method of claim 32, wherein providing the bottom metal reflectorlayer comprises depositing and patterning the bottom metal reflectorlayer.
 35. The method of claim 32, wherein providing the flexure layerand the top metal reflector layer comprises depositing the flexurelayer, depositing the top metal reflector layer on the flexure layer,and patterning the flexure layer and the top metal reflector layer. 36.The method of claim 32, wherein providing the flexure layer and the topmetal reflector layer comprises depositing the top metal reflectorlayer, depositing the flexure layer on the top metal reflector layer,and patterning the flexure layer and the top metal reflector layer. 37.The method of claim 32, wherein removing the first filler material andthe second filler material comprises performing isotropic cleanoutetching.
 38. A display device constructed at least in part by performinga method comprising: providing a bottom metal reflector layer on asilicon substrate layer of the display device; depositing and patterningfirst filler material on the bottom metal reflector layer; providing aflexure layer and a top metal reflector layer on the first fillermaterial; providing an oxide pixel plate layer on the flexure layer andthe top metal reflector layer; depositing and patterning second fillermaterial on the oxide pixel plate layer; depositing an oxide layer onthe second filler material; defining one or more vias through the secondfiller material; and, removing the first filler material to defineindividually controllable optical cavities between the first and the topmetal reflector layers, and the second filler material to define aircavities between the oxide pixel plate layer and the oxide layer. 39.The display device of claim 38, further comprising, after providing thebottom metal reflector layer, depositing an oxide dielectric layer. 40.The display device of claim 38, further comprising providing aprotective layer over the oxide layer.
 41. The display device of claim40, further comprising providing an anti-reflective coating over theprotective layer.
 42. The display device of claim 40, further comprisingsputtering an absorbing layer over the protective layer.